Another residential solar power system malfunctioned!
According to the Rostock Police Headquarters in Germany, a fire broke out at 3 PM on July 5th in a wooden shed within the yard of a detached house in Bentwisch.
The investigation indicates that a battery storage module in an installed solar power system inside the shed overheated and ignited the fire. An explosion occurred during firefighting efforts, blowing off the roof and causing the entire structure to collapse. Three volunteer firefighters sustained minor injuries from the explosion. Flying debris also damaged two adjacent properties. The estimated damage is approximately €40,000.
Following the incident, police cordoned off the scene. The fire department deployed an excavator and a large water tank to submerge the exploded battery debris in water to prevent further chemical reactions.
A total of 75 firefighters from five volunteer fire brigades—Bentwig, Klein Kussewitz, Mönchhagen, Poppendorf, and Rövershagen—were deployed to the rescue operation. The prosecutor's office has ordered the dispatch of experts to determine the cause of the fire, and the criminal police have opened an investigation.
Regarding the explosion, Jörg Westphal, deputy captain of the Neustrelitz volunteer fire brigade, explained that photovoltaic equipment is unique in that, in addition to conventional alternating current, it also contains a direct current circuit, with current flowing from the photovoltaic modules to the inverter. Furthermore, this power generation system continuously produces electricity based on real-time sunlight intensity.
Based on the situation, the explosion was most likely caused by overcharging of the photovoltaic-energy storage system. (Photovoltaic overcharge explosions typically refer to explosions caused by thermal runaway of the energy storage battery due to overcharging in a "photovoltaic + energy storage" system. The core causes are often electrical system malfunctions or battery management failures.)
Residential photovoltaic-energy storage system explodes twice in two years!
This explosion of a photovoltaic system in a German villa is not an isolated incident. Just last year, also in Germany, a villa with a photovoltaic system experienced an explosion.
Around February last year, a serious explosion occurred in Schleswig-Holstein, Germany. A residential building was severely damaged; photos from the scene show significant damage to the exterior walls.
The local volunteer fire brigade reported: "A loud bang, by a pressure wave. Then thick smoke rose." It is understood that although multiple parts of the building caught fire, the fire was quickly brought under control. Fortunately, the severely damaged building was vacant at the time of the incident, but it may be demolished later.
It is understood that this was a detached villa equipped with photovoltaic (PV) and energy storage facilities. According to NDR (North German Broadcasting), preliminary investigations indicate that the explosion was caused by a malfunction in the PV-storage system. At noon that day, the PV power had fully charged the energy storage system, but the remaining electricity was not fed into the grid and continued to power the storage batteries, leading to the explosion.
This explosion is highly similar to last year's, leading some industry insiders to believe that the cause of the residential PV explosion is most likely due to overcharging, just like last year.
What are the potential risks of residential solar PV and energy storage systems?
As is well known, there are significant differences in the operation and use of residential solar PV systems in China and overseas. In China, the majority of the residential solar PV market is in rural areas, especially in northern provinces with abundant sunshine, such as Hebei, Henan, and Shandong. The large and concentrated villages and towns provide ample opportunities for residential solar PV installations.
However, overall electricity consumption in rural China is relatively low, and residents' peak electricity consumption is mostly at night when solar power is not generating electricity. Combined with the relatively low cost of electricity for residents, the electricity generated by these residential solar PV systems is primarily fed into the grid. Residents can earn income by sharing the revenue from selling the electricity or simply renting out their rooftops.
The situation is different overseas, especially in Europe, where high electricity prices are the norm. Residential electricity costs are several times higher than in China. Therefore, European users typically install energy storage alongside their solar PV systems to form a complete system. The electricity generated by the solar PV systems is primarily for self-consumption, thus mitigating the high electricity bills.
Therefore, integrated photovoltaic (PV) and energy storage power generation systems are popular in markets with high electricity prices. Furthermore, compared to residential PV systems in China, many villas in Europe use off-grid PV systems, meaning these systems are not connected to the grid and are solely for self-consumption. The overcharging risks of PV systems often originate from off-grid systems.
Currently, off-grid PV power plants in Europe are not limited to the residential market. For example, they are used in the French Alps, a farm in Austria, and a brewery in Poland.
Off-grid PV power plants, due to their components including PV panels, energy storage batteries, inverters, and complex electrical wiring, and often installed outdoors or on rooftops, also present various safety hazards.
As is well known, off-grid PV power plants pose a risk of high-voltage direct current (DC) electric shock. The DC voltage after PV panels are connected in series can reach hundreds of volts, far exceeding the safe voltage for the human body. Live operation, incorrect wiring, or insulation damage can easily cause fatal electric shocks; DC arcs are difficult to extinguish and can easily cause severe burns.
In addition, loose wiring, overheating of inferior cables, sparking at joints, and poor heat dissipation in inverters and controllers can all cause fires. The "hot spot effect" caused by bird droppings, dust, or other localized shading of photovoltaic panels can lead to a rapid increase in localized temperature, causing module burnout or fires.
Besides the photovoltaic equipment, the most vulnerable part of an off-grid photovoltaic system is the energy storage battery.
Firstly, in terms of installation, poor ventilation, high temperatures, and dampness in residential energy storage systems will accelerate battery aging and increase the risk of flammable gas explosions or electrical leaks. Countries like Germany, Austria, and Switzerland, which installed photovoltaic systems early on, have entered the post-grid era, and newly installed photovoltaic power generation systems generally adopt off-grid mode. Their installation specifications require energy storage batteries to be placed outdoors or in a basement with a dedicated fire door.
Furthermore, the quality of the purchased energy storage products is crucial. Mixing new and old batteries, batteries of different brands and capacities can lead to uneven charging and discharging, causing overcharging and over-discharging, shortening battery life, and increasing the risk of fire. Common causes of overcharging in photovoltaic systems include BMS management system failure, charging equipment malfunction, or improper operation and maintenance.
Currently, in addition to conventional residential solar PV systems, balcony solar PV is also gaining popularity in Europe. While not as large in scale as traditional rooftop solar PV, it still presents significant potential risks.
When a user installs a balcony solar PV system, when sunlight is abundant and the power generation exceeds the household's current electricity demand, the excess electricity flows back into the public grid, creating a backflow.
While feeding excess electricity back into the grid from a balcony solar system might seem like efficient resource utilization, this "backflow" is actually prohibited and carries multiple risks for balcony solar PV systems that haven't undergone formal grid connection procedures. Therefore, without anti-backflow devices, these balcony solar PV systems could become a "hidden killer" of the power grid.
This German case once again highlights the potential safety hazards of residential solar PV systems. For users, while solar power plants are an important driver of clean energy, reliable products and proper maintenance are equally crucial for safety.
